Conventional television receivers are designed and configured to optimize the display quality of video program material. For example, in the United States, televisions are typically optimized to display NTSC and/or S-video signals from sources such as television antennas, video cassette recorders, digital satellite television receivers and/or cable television sources. Under some circumstances, however, it is desirable to display computer or computer-like generated images on a television receiver. For example, modern video conferencing systems often combine video signals (which may be formatted according to any of a variety of video signal transmission standards) with computer graphic signals (such as are used to display a variety of control buttons, etc.). Because the television is configured to optimize the display of conventional video signals, however, the resultant display of computer-generated images may be less than satisfactory.
To overcome some of these problems, some television receivers employ video encoders to convert computer-generated image signals into conventional NTSC signals before displaying the computer generated images. FIG. 1 illustrates such a system 10. As shown, a computer-generated image 12 may be provided to a television receiver 14 through a video encoder 16. Video encoder 16 may be part of television receiver 14 or it may be housed within the computer system that generated the image 12. Alternatively, video encoder 16 may be a stand-alone unit. Regardless of the configuration though, video encoder 16 generally operates by converting the (typically) VGA/RGB signals which make up computer-generated image 12 into conventional NTSC or S-video signals (in Europe or other areas, PAL signals may be provided for display by television receiver 14. The NTSC or S-video signals are typically provided to television receiver 14 through a compatible input port 18 on television receiver 14.
Although this arrangement may alleviate some of the problems associated with the display of computer-generated images on televisions, it does have some undesirable side effects. First, because televisions are generally setup to overscan the picture, i.e., televisions typically do not display the entire image broadcast by the video source, and computer images use the entire visible raster (e.g., on a computer video monitor), system 10 will not display the outer edges of the computer-generated image 12. This may be compensated for through manual control inputs 20 which may be used to adjust the picture size to accommodate the entire computer generated image 12. However, this will have the drawback of effectively shrinking the display area of television receiver 14. Further, additional control inputs 20 will be required when television receiver 14 is used to display conventional television video input signals (e.g., from a cable television source) to recover the original display size. Second, because tile picture quality of a conventional television receiver degrades rapidly at the edges of the display, computer-generated material at the edges of the of the display (which may often be text, e.g., for a menu) will be displayed poorly. Third, the user must manually switch the television to display the images received through port 18.